Carbon nanotubes (CNTs) possess a variety of useful properties, including high thermal conductivity, tensile strength, and elastic modulus. Carbon nanotubes have been investigated for applications in nanotechnology, electronics, optics, and other fields of materials science and technology.
CNTs exhibit high thermal conductivity, with multi-wall carbon nanotubes (MWCTs) exhibiting thermal conductivities up to about 3,000 W/mK at room temperature, and single-wall carbon nanotubes (SWNTs) exhibiting thermal conductivities up to about 5,000 to about 8,000 W/mK at room temperature. As a result, CNTs, especially vertically aligned arrays of CNTs, have attracted significant interest for use in thermal interface materials (TIMs). In order to function efficiently and maintain performance over time, the CNTs should be well anchored to a support structure, uniformly aligned, preferably perpendicular to the support surface, and be present at a high density on the support structure.
However, in spite of the tremendous potential of such materials, it has proven difficult to form dense and well aligned CNT arrays on metal surfaces, and to achieve good adhesion between the metal and CNTs. Typically, arrays of aligned carbon nanotubes are grown from surfaces containing a thin film (<1 nm thick) of catalyst, such as iron, supported on a metal oxide film, such as alumina, with a thickness of between 10 and 200 nm. Under growth conditions, the catalyst forms small (<10 nm) islands or particles on the surface of the oxide film from which the nanotubes grow. The catalyst particles pack on the surface, constraining the nanotube growth to a direction perpendicular to the surface.
Unfortunately, CNT arrays grown from these surfaces display limited density and yield. This is the result of migration of the catalyst particles into the oxide film during the course of nanotube growth. See, for example, Amama, P. B. et al. ACS Nano, 4:895-904 (2010) and Kim, S. M. et al. J. Phys. Chem. Lett. 1:918-922 (2010). In addition, CNT arrays formed in this fashion are generally poorly adhered to underlying metal surfaces, because the oxide layer, incorporated to promote dense and aligned CNT growth, does not adhere well to the underlying metal surface.
In order to provide improved CNT arrays for use as thermal interface materials (TIMs), CNT arrays with higher nanotube density and improved nanotube adhesion are required.
Therefore, it is an object of the invention to provide surfaces for the growth of high density arrays of carbon nanotubes, and methods of use thereof.
It is a further object of the invention to provide arrays of vertically aligned CNTs which are well adhered to a surface, such as a metallic surface.
It is also an object of the invention to provide arrays of vertically aligned arrays of CNTs for use as thermal interface materials (TIMs).